Towards a determination of absolute cross sections for projectile excitation of hydrogen-like uranium in collisions with neutral atoms

Recently, the contribution of the generalized Breit interaction to electron impact ionization was identified for the first time in a high-Z system, namely, hydrogen-like uranium. This study employed a measurement of the relative population of the j = 1/2 and j = 3/2 states of the L shell by projectile excitation in collision of U⁹¹⁺ with hydrogen and nitrogen targets. However, for a rigorous test of ion–atom collision theory, also the absolute excitation cross sections are of great importance. In the present work, we report on our efforts to extend the previous study to a determination of the absolute projectile excitation cross sections by normalization to the well-known radiative electron capture process.     

A simple approach to prepare monodisperse mesoporous silica nanospheres with adjustable sizes

A new and facile approach has been developed to prepare monodisperse mesoporous silica nanospheres (MMSNs) with controlled particle sizes and pore structures. In our approach, MMSNs were synthesized simply in a sodium acetate solution without adding any other alkali or alcohol additives. MMSNs have a spherical shape and uniform particle sizes, which can be adjusted from 50 to 110 nm by increasing the reaction temperature from 40 to 80 °C. By performing a subsequent hydrothermal treatment (HT) under basic condition (pH=~11.5) at 130 °C, the mesoporous pore volume and surface area can be enhanced, while keeping the mono-dispersion characteristics and the mesopore size almost unchanged. The pore sizes of MMSNs can be adjusted from 2.8 to 4.0 nm under acidic solutions by changing the HT temperature from 100 to 130 °C. The formation process of MMSNs has been investigated by transmission electron microscopy (TEM) and attenuated total reflection Fourier transform infrared (ATR-FTIR) techniques. A spherical micelle templating mechanism is proposed to explain the formation of MMSNs in our system, which is different from that of traditional highly ordered mesoporous silica nanoparticles (MCM-41).     

Interstitial solute diffusion in metals

The diffusion of interstitial solute atoms, which were subject to nearest neighbour solute-solute interactions, was simulated by means of a modified Monte Carlo method. Solute correlation factors, nearest neighbour vacancy availability factors and effective jump frequency factors were calculated as functions of composition and temperature. Compared with non-interacting atoms attraction between solute atoms always retarded diffusion whereas repulsion always enhanced diffusion except within the ordered region.     

Photoelectron-spectroscopic determination of lattice self-potentials in lanthanide trifluorides

Since the photoelectron spectroscopically measured binding energies probe the potentials at the cation and anion sites separately in solids, they should be a direct determination of the lattice self-potentials at these sites through comparisons with the respective ionization potentials of the gaseous ions. In a study of the photoionization of the 1s orbital electrons on the fluoride ion and of the outer 5p or 4f orbital electrons on the cations of the lanthanide trifluorides, it is found that the so determined lattice self-potentials at the anion sites deviate from those calculated from the electrostatic interactions in the point charge model by an amount which can be explained in terms of ionicity. For the cations, however, the deviations for all except La³⁺ and perhaps Gd³⁺ exceed those expected for ionicity in the point charge model by as much as 2.3 eV in the case of the maximum at Pr³⁺. These deviations are discussed in terms of crystal field interactions, covalency, polarization, and complication caused by final state relaxation during photoionization.     

Electromagnetic self-energy of quarks confined to a sphere

We calculate the electromagnetic energy shift, δω, of a massless fermion confined to a sphere. We find δω > 0, in agreement with our previous result for a slab, and in disagreement with the sign needed to obtain the right value of the neutron-proton mass difference in a model in which the hadron consists of confined massless quarks. We consider the effect of a bare mass for the confined quarks, and show that it is then possible for δω to be negative.     

Diophantine approximation and badly approximable sets

Let (X,d) be a metric space and (Ω,d) a compact subspace of X which supports a non-atomic finite measure m. We consider ‘natural’ classes of badly approximable subsets of Ω. Loosely speaking, these consist of points in Ω which ‘stay clear’ of some given set of points in X. The classical set Bad of ‘badly approximable’ numbers in the theory of Diophantine approximation falls within our framework as do the sets Bad(i,j) of simultaneously badly approximable numbers. Under various natural conditions we prove that the badly approximable subsets of Ω have full Hausdorff dimension. Applications of our general framework include those from number theory (classical, complex, p-adic and formal power series) and dynamical systems (iterated function schemes, rational maps and Kleinian groups).     

An exact operator solution of the quantum Liouville field theory

Exact, closed form results are given expressing the quantum Liouville field theory in terms of a canonical free pseudoscalar field. The classical conformal transformation properties and a Bäcklund transformation of the Liouville model are briefly reviewed and then developed into explicit operator statements for the quantum theory. This development leads to exact expressions for the basic operator functions of the Liouville field: ?_μΦ, and e^nΦ. An operator product analysis is then used to construct the Liouville energy-momentum tensor operator, which is shown to be equal to that of a free pseudoscalar field. Dynamical consequences of this equivalence are discussed, including the relation between the Liouville and free field energy eigenstates. Liouville correlation functions are partially analyzed, and remaining open questions are discussed.     

The Amyloid Fibril-Forming β-Sheet Regions of Amyloid β and α-Synuclein Preferentially Interact with the Molecular Chaperone 14-3-3ζ

14-3-3 proteins are abundant, intramolecular proteins that play a pivotal role in cellular signal transduction by interacting with phosphorylated ligands. In addition, they are molecular chaperones that prevent protein unfolding and aggregation under cellular stress conditions in a similar manner to the unrelated small heat-shock proteins. In vivo, amyloid β (Aβ) and α-synuclein (α-syn) form amyloid fibrils in Alzheimer’s and Parkinson’s diseases, respectively, a process that is intimately linked to the diseases’ progression. The 14-3-3ζ isoform potently inhibited in vitro fibril formation of the 40-amino acid form of Aβ (Aβ₄₀) but had little effect on α-syn aggregation. Solution-phase NMR spectroscopy of ¹⁵N-labeled Aβ₄₀ and A53T α-syn determined that unlabeled 14-3-3ζ interacted preferentially with hydrophobic regions of Aβ₄₀ (L11-H21 and G29-V40) and α-syn (V3-K10 and V40-K60). In both proteins, these regions adopt β-strands within the core of the amyloid fibrils prepared in vitro as well as those isolated from the inclusions of diseased individuals. The interaction with 14-3-3ζ is transient and occurs at the early stages of the fibrillar aggregation pathway to maintain the native, monomeric, and unfolded structure of Aβ₄₀ and α-syn. The N-terminal regions of α-syn interacting with 14-3-3ζ correspond with those that interact with other molecular chaperones as monitored by in-cell NMR spectroscopy.